The present invention relates generally to magnetoresistive read sensors for use in magnetic read heads. In particular, the present invention relates to a planar double spin valve read head with narrow shield-to-shield spacing and enhanced giant magnetoresistance (GMR) effect.
A magnetic read head retrieves magnetically-encoded information that is stored on a magnetic medium or disc. The magnetic read head is typically formed of several layers that include a top shield, a bottom shield, and a read sensor positioned between the top and bottom shields. The read sensor is generally a type of magnetoresistive sensor, such as a GMR read sensor. The resistance of a GMR read sensor fluctuates in response to a magnetic field emanating from a magnetic medium when the GMR read sensor is used in a magnetic read head and positioned near the magnetic medium. By providing a sense current through the GMR read sensor, the resistance of the GMR read sensor can be measured and used by external circuitry to decipher the information stored on the magnetic medium.
A common GMR read sensor configuration is the GMR spin valve configuration in which the GMR read sensor is a multi-layered structure formed of a ferromagnetic free layer, a ferromagnetic pinned layer and a nonmagnetic spacer layer positioned between the free layer and the pinned layer. The magnetization direction of the pinned layer is fixed in a predetermined direction, generally normal to an air bearing surface of the GMR spin valve, while a magnetization direction of the free layer rotates freely in response to an external magnetic field. An easy axis of the free layer is generally set normal to the magnetization direction of the pinned layer. The resistance of the GMR read sensor varies as a function of an angle formed between the magnetization direction of the free layer and the magnetization direction of the pinned layer. This multi-layered spin valve configuration allows for a more pronounced magnetoresistive effect than is possible with anisotropic magnetoresistive (AMR) read sensors, which generally consist of a single ferromagnetic layer.
Typically, the magnetization of the pinned layer is fixed in the predetermined direction by exchange coupling an antiferromagnetic layer to the pinned layer. The antiferromagnetic layer is positioned upon the pinned layer such that the antiferromagnetic layer and the free layer form distal edges of the GMR spin valve. The spin valve is then heated to a temperature greater than a Nxc3xa9el. temperature of the antiferromagnetic layer. Next, a magnetic field oriented in the predetermined direction is applied to the spin valve, thereby causing the magnetization direction of the pinned layer to orient in the direction of the applied magnetic field. The magnetic field may be applied to the spin valve before the spin valve is heated to the temperature greater than the Nxc3xa9el temperature of the antiferromagnetic layer. While continuing to apply the magnetic field, the spin valve is cooled to a temperature lower than the Nxc3xa9el temperature of the antiferromagnetic layer. Once the magnetic field is removed from the spin valve, the magnetization direction of the pinned layer will remain fixed, as a result of the exchange with the antiferromagnetic layer, so long as the temperature of the spin valve remains lower than the Nxc3xa9el temperature of the antiferromagnetic layer.
The magnetic shields of a GMR read head block stray fields from the magnetic medium, and thereby allow for an increase in the on-track spatial resolution (i.e., linear density), typically measured in bits per inch or BPI. The shield-to-shield spacing limits the linear density of a high density head.
The gap layers, which are positioned between the shields, must be maintained at an appropriate thickness to ensure proper isolation. Therefore, there is a limit to the amount the shield-to-shield spacing can be reduced by reducing the thickness of the gap layers. By reducing the sensor thickness, the shield-to-shield spacing may be further reduced.
Existing spin valves have a vertical structure in which the various layers are stacked vertically between the shields. By stacking all of the layers of the spin valve on top of each other between the shields, the shield-to-shield spacing can, only be made as narrow as the entire spin valve stack (plus the gap layers). It would be desirable to use a planar spin valve wherein less than all of the layers of the spin valve stack are positioned between the shields in a central region of the head. Such a spin valve read head would provide a reduced shield-to-shield spacing since the shields would be separated by only one or two layers of the spin valve stack, rather than all of the layers of the stack.
It would also be desirable to increase the GMR effect by using a double spin valve structure operating in a current perpendicular to plane mode or CPP mode.
A planar spin valve read head comprises a top and a bottom shield, and a first and a second gap layer. The first gap layer is positioned adjacent to the bottom shield. The second gap layer is positioned adjacent to the top shield. The read head includes planar sensor means positioned between the first and the second gap layers for sensing a magnetic field from a magnetic medium.
In a preferred embodiment, the planar sensor means comprises a first and a second planar spin valve, which share a common free layer and operate in a current perpendicular to plane (CPP) mode. The planar spin valve read head of the present invention provides a reduced shield-to-shield spacing to accommodate high linear densities, as well as an enhanced GMR effect.